Designing Trimetallic Single-Doped Alloy Catalysts for Sustainable Ammonia Production: The Role of Dopants in Active Site Engineering

Using in-depth density functional theory (DFT) calculations, this study investigated the (111) surfaces of trimetallic single-doped alloys (SDAs) based on the CuNi alloy doped with Ag, Au, Pd, Pt, Co, Ru, and Fe, evaluating their catalytic potential for ammonia synthesis. This study analyzed their activity and selectivity toward N2 and H2, as well as the rate-limiting steps in associative and dissociative reaction pathways. Among the various dopants, Au was the most effective for the associative pathway, enhancing charge transfer to the N2 molecule and lowering the N2H formation energy barrier. Meanwhile, Pd and Pt showed better performance in suppressing the hydrogen evolution reaction. The spillover energy (SOE) and dopant charge, known as key descriptors of the catalytic performance in bimetallic SDAs, were also evaluated to determine their applicability in trimetallic SDAs. The findings highlight that, unlike in bimetallic SDAs, where dopant charge governs performance, the N2 activity of trimetallic SDAs depends not only on the dopant charge but also significantly on the dopant’s local environment (the dopant’s nearest neighbor atoms). This difference is due to the random arrangement of two different metal atoms in the bimetallic host of SDA surfaces, resulting in variations in the charge distribution around the dopant depending on where it is placed. Although SOE failed to capture the influence of the dopant’s local environment accurately, it effectively determined the ability of the dopant to catalyze the rate-limiting steps of the nitrogen reduction reaction by directing the intermediates from the dopant to the host atoms. Overall, this study demonstrates that the SOE and dopant charge, while important, are not sufficient for designing trimetallic SDA catalysts for ammonia synthesis. Instead, the dopant’s local environment must also be taken into account. This work establishes fundamental guidelines for engineering advanced trimetallic SDA catalysts tailored for ammonia production.